Both harmful and beneficial bacteria live in and on people's bodies. Lactobacillus is one of the so-called 'good' bacteria, found in the vaginas of 80 to 90 percent of healthy women. However, some research has indicated that women infected with HIV have altered levels of this and other beneficial bacteria present in their vaginas. Rose Hoban reports.

Obstetrician Jane Hitti from the University of Washington says these good bacteria have been shown to help protect against other kinds of vaginal infections, such as sexually-transmitted infections like herpes, chlamydia and gonorrhea, as well as other kinds of bacterial infections like bacterial vaginosis.

Hitti says she thought lactobacillus might also be effective at controlling the amount of HIV present in the vaginas of HIV-positive women. So she and her co-investigators followed several dozen HIV-positive women for five years to track amounts of Lactobacillus and HIV in their vaginas.

"We found, first of all, that at any given time, only about half of the women carried the healthy bacteria, the Lactobacillus, in the vagina," Hitti reports. "And we found that when they had the Lactobacillus present, they had less HIV present in the vagina, and that this was true even after we took into account other factors, like the amount of HIV in the blood, and whether or not they were on treatment for HIV."

Hitti also noted that levels of vaginal lactobacillus in any one woman varied over time. In other words, more good bacteria meant less HIV and, conversely, less meant more HIV.

Hitti says she was surprised at how strong the association between the two seemed to be, and how consistent the relationship was over time.

"When we started this project, we thought that maybe the 'bad' bacteria in the vagina were going to have more of an effect on the amount of HIV than the good bacteria," Hitti says. "But, really, as we looked at this analysis, it really seems like the good bacteria were key, and the effects of the bad bacteria were kind of secondary."

Hitti says this could have important implications for controlling levels of HIV in the female genital tract and could contribute to whether or not a woman passes HIV to a sexual partner, or a child being born.

Hitti also says knowledge about beneficial bacteria could help in the development of microbicides that could reduce HIV transmission between sexual partners.

She recently presented her research at the Conference on Retroviruses and Opportunistic Infections.